Blowout fuse with disintegrating end closure



Nov. 9, 1965 G. D. SMITH ETAL 3,217,126

BLOWOUT FUSE WITH DISINTEGRATING END CLOSURE Filed Dec. 31, 1962 2 Sheets-Sheet l INVENTORS GERALD D. SMITH F I G. 3. BY HARLEY RWANTZ JR.

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ATTORNEYS BLOWOUT FUSE WITH DISINTEGRATING END CLOSURE Filed Dec. 31, 1962 Nov. 9, 1965 G. D. SMITH ETAL 2 Sheets-Sheet 2 F I G. 5

INVENTORS GERALD D. SMITH BY HARLEY R.WANTZ JR. JM%*7 7 ALKOBNEYS ail FIG.6.

United States Patent 3,217,126 BLOWOUT FUSE WITH lDISlNTEGRATING END CLOSURE Gerald D. Smith, St. Louis, and Harley E. Wantz, Jr.,

Rock Hill, Mo., assignors to James R. Kearney Corporation, St. Louis, Mo., a corporation of Delaware Filed Dec. 31, 1962, Ser. No. 248,783 1 Claim. (Cl. 200-432) This invention relates to electric fuses and more particularly to heavy duty fuses primarily intended for use in electric service or distribution systems' One example of this use is a fuse cutout. These devices are usually provided with a fixed and a movable contact, the latter of which is on a movable end of a fuse tube and is engageable with and disengageable from the fixed contact. A terminal fitting for an electric conductor is directly connected to the fixed contact. The opposite end of the fuse tube usually has a hinged mounting, or the like, on the device spaced from the fixed contact and is electrically connected to another terminal fitting for an electric conductor. Within the fuse tube, which is an insulator, is a fuse link conductor extending from end to end of the tube and electrically connected to the movable contact and the terminal fitting at the hinged end of the device to complete the circuit between the two terminals when the contacts are engaged. The fuse link, itself, is constructed to have a given amperage rating within a given voltage range. On the upper end of the fuse tube is a closure in the form of a cap. The cap anchors one end of the fuse link to the fuse tube, and the assembly of fuse link, fuse tube and cap, together make a fuse cartridge open at the lower end opposite the cap to vent low internal gas pressures developed within the tube occurring during a low amperage fault and through which the tail portion of the fuse link may be expelled by gas pressures. A high amperage fault will most certainly develop gas pressures internal of the tube which require vents at both ends to prevent tube rupture. Since such a failure of the tube would be dangerous, it must be avoided, consequently, it is desirable to design the cap to open instantaneously at high internal gas pressures developed within the tube and experienced during such occurrences as a high amperage fault. This will relieve the pressure from both ends of the tube. Although many attempts have been made in the past to develop a cap which will relieve internal pressures instantaneously if a certain internal gas pressure is reached, or exceeded, within the tube, these have not been entirely successful when applied to a product manufactured by processes required to achieve volume and low cost. Caps have been known for many years which were formed, generally speaking, of two parts, one of which was rupturable at high gas pressures, or one of which was separable from the other due to deformation in the one part or the other.

It is one of the objects of this invention to provide a disk-like closure for a vent which will disintegrate on failure and rapidly relieve excess gas pressure.

It is another object of this invention to provide a disk which will burst into fragments when subjected to the unbalanced force produced by a fluid pressure.

It is another object of this invention to provide disks which will burst into fragments when subjected to an unbalanced force produced by substantially the same fluid pressure acting on a given area of one side thereof.

It is another object of this invention to provide a cap for an electric fuse tube having a cap end wall which will burst into fragments when subject to the force of fluid pressure caused by a high current fault during fuse burn up.

Patented Nov. 9, 1965 It is still another object of this invention to provide caps for electric fuse tubes having cap end walls which will burst into fragments when subject to the force of substantially the same fluid pressure produced by a current fault causing fuse burn up.

This invention is based upon certain incidental discoveries made while pursuing an investigation into the properties of certain materials. These incidental discoveries revealed properties inherent in commercially produced sintered metals, such as brass and bronze alloys. One of these discovered properties is that sintered metals shatter into fragments on failure when subject to a relatively uniformly distributed force in excess of their strength. Fluid under suflicient pressure, when imposed upon a sufficient area of a sintered metal disk, will cause a failure of the disk in which the disk disintegrates. Further investigation revealed that for a .given area the fluid pressure required to produce that failure could be predicted very closely from testing a few samples.

These discoveries made possible a new and superior product in the form of a disk-like closure for a vent which could be depended on to relieve excess fluid pressure by completely opening the vent on failure when subject to a predetermined fluid pressure. One aspect of this discovery was the uniformity in bursting strength of such material. The other aspect of this discovery was the fragmentation of the material on bursting. With respect to this aspect, it is contemplated that other materials possess the same property of complete fragmentat1on on failure. This suggests that other materials, such as tempered glass, which is known to have this property, could be substituted in some applications provided, of course, like the sintered metal, the bursting pressure required was within the desired range in a disk of proper dimensional limits to give the required mechanical characteristics to suit the application.

Other objects and advantages of this invention will appear in the following detailed description which is in such clear, concise and exact terms as will enable anyone skilled in the art to make and use the same when taken in conjunction with the accompanying drawings, forming a part thereof, and in which:

FIG. 1 is an environmental view in side elevation illustrating a fuse cutout equipped with a cap construoted in accordance with the instant invention;

FIG. 2 is a front elevational view partly in section illustrating a fuse cap constructed in accordance with this invention;

FIG. 3 is a top plan view of the fuse cap shown in FIG. 2;

FIG. 4 is a fragmentary view partly in section of the upper end of the fuse cartridge shown in FIG. 1;

FIG. 5 is a view similar to FIG. 4 showing the position of the parts after the cap has ruptured due to a high current fault; and

FIG. 6 is a view similar to FIG. 4 illustrating a modified form of fuse cap.

With reference now to FIG. 1, the numeral 1 designates a metallic bracket, the left end of which is normally mounted on suitable supporting structure, such as a pole cross arm, not shown, by a clamping plate 2 and bolts 3 and 4. Adjustably secured on the projecting arm of the bracket 1 is a hanger 5 secured to the bracket 1 by a clamping bolt 6. The downturned arm 7 of the hanger 5 supports a clamp 3 secured around an insulator 9 by the bolt 11 and to the downturned end of bracket 5 by a set screw 12.

On the upper end of insulator 9, there is mounted a fixed terminal part 14 mounted on the top of the insulator 9 by a suitable clamping ring 15. Terminal 14 carries a T-bolt 17 to which a line conductor may be secured. Projecting outwardly from the terminal 14 is a fixed latch part 19 which is formed in the shape of a sleet hood to protect the latch. Extending wings 20, one of which is shown, guide the movable part of the latch into the fixed latch 19.

The bottom end of the insulator 9 carries a terminal 22 provided with a T-head bolt 23 to which a line conductor may be secured. On the bottom terminal 22 is a clamping ring 24 which fixes the terminal 22 to the lower end of the insulator 9. Projecting in the opposite direction from the clamping ring 24 are a pair of jaws 25 which are spaced apart. A pair of trunnions 26 are hingedly mounted in the jaws 25 and the trunnions 26 are carried by an arm 27 which has forked ends 28 supporting the lower end of the fuse tube 30. Hinged on the arm 27 is a bracket 31 having a clamping ring 32 embracing the fuse tube and secured thereto. The bracket 31 has an arm 33 provided with an eye 34 through which the end of a switch stick may be inserted to remove and replace the bracket 31 and its connected parts.

The upper end of the fuse tube is secured in a clamping ring 35. On one side of the ring 35 is a pull out loop 36 and on the other side is an integrally formed movable latch part 37.

Within the fuse tube 30 is a fuse link 39. This fuse link 39 electrically connects with the metal neck portion 40 extending from the upper end of the clamping ring I 35. This portion of the extension 40 is threaded at its end to receive a fuse cap 41 which contains the buttonlike head 55 at the upper end of the fuse link and closes the upper end of the fuse tube 30. The lower end of the fuse link 39 has a tail portion which passes out of the open lower end of the fuse tube 30 between the forked ends of the arm 27 and is secured beneath a thumb screw 43 on the arm 27. A U-shaped spring contact 44 connects the terminal 22 with the end of the arm 27 concealed within the jaws 25 thereby completing the circuit from the fixed terminal 14 to the fixed terminal 22.

The above described structure of the fuse cutout forms no part of the instant invention, but is included here merely to illustrate one use of the invention which is confined to the fuse cap structure 41. The fuse cutout, itself, is a standard piece of equipment and its operation is well understood in the art and will not be explained in detail here. Suffice to say that the fuse cutout operates in the same manner as described in the patent to Fox, 2,047,365, of July 14, 1936.

The fuse cap construction alone is shown more specifically in FIGS. 2 and 3. With reference to these figures of the drawings, fuse cap 41 has a cylindrical skirt 45 knurled on its outside surface as at 46 to provide for manual manipulation. Skirt 45 is provided with internal threads 47 which extend to cylindrical part 49. The upper edge of the skirt 45 may be provided with an internal flange 54 if desired. Seated within the cylindrical portion 49 is a disk 51 of sintered metal, preferably sintered brass or bronge alloy. This disk 51 is held in place by a suitable cement 53 filling the cavity between the top of the disk 51 and the internal flange 50. It is preferred that the cement 53 be an epoxy resin, or the like, so as to make a firm bond between the top of the disk 51 and the skirt 45.

Turning now to FIG. 4, it will be noted that parts corresponding to those shown in FIG. 1 have been given the same reference character. As will be obvious from this illustration, the fuse tube 30 contains the fuse link 39 which has a button-like head 55 seated on the upper surface of the neck 40. This button-like head 55 is held in place by threading the cap 41 onto the upper threaded end of the neck 40 so that the disk 51 contains the button-like head 55 captive in the top of the fuse tube 30. The assembly of fuse tube, fuse link and cap 41 forms the cartridge of t e fuse, The electrical connection between the fuse link 35 and the clamping sleeve 35 is formed by the contact between the lower surface of the button-like head 55 and the neck 40.

In the device depicted in FIG. 4, the tension in the fuse link 39 forcibly retains the button 55 in electric contact with the fitting 40 so that the electric circuit is through the fuse link 39, button 55, fitting 4t) and fixed latch 37. If it is desired, the cap 41 may be so threaded that the frangible disk 51 will contact the top of the button head 55 and also aid in firmly holding the button head in contact with the fitting 40.

It will be understood that with the construction, as shown in FIG. 4, the frangible disk 51 has a strength sufiicient to remain intact during a low current fault and that the vent opening at the bottom of the fuse tube 30 is sufficient to prevent undue rise in gas pressures within the tube under such circumstances. The gas pressure developed, however, will certainly be sutficient to aid in blowing out the tail of the ruptured fuse link 39. This in turn releases the articulated connection between arm 27 and bracket 31. When this occurs, arm 27 will pivot on the pintles 26 with respect to the bracket 31 to release the latch parts 19 and 37 allowing the cartridge to swing downwardly and outwardly until it hangs in inverted position from the jaws 25.

The action during a high current fault will be very similar except for the fact that the gas pressure developed within the fuse tube 30 will exceed the designed strength of the frangible disk 51. As shown in FIG. 5, the button head 55 will be blown from the fuse tube 30 as the disk 51 disintegrates into small fragments on failure. The disintegration of the disk 51 into small fragments fully opens the vent from the tube 30 to dissipate the gas pressure instantaneously. In this respect, the function of the disk 51 differs from all prior constructions. On failure, disk 51 completely disintegrates, and the button head is blown out of the fuse tube completely opening the vent passage. This result has been realized only partially by the prior constructions now available commercially. Both the material, or characteristics of the material, in the disk 51 and the gas tight joint formed by the cement seem to contribute to the uniform results obtained by the instant invention. The disk being of sintered material, it is a mixture of minute particles of material united under heat and pressure. When it fails, the disk 51 will fail totally rather than only partially. These partial failures, which have been often experienced with prior devices, require compromises in the design and construction of the closure which minimize the advantages to be gained by venting both ends of the fuse tube 30.

FIG. 6 shows a modified construction for the closure. Like parts in this view are indicated by the same reference character. The closure 61 has a threaded skirt 62 which terminates at an internal annular flange 64 surrounding the upper end of the skirt. The annular flange 64 and an annular flange 65 together form a seat for a disk of frangible material, indicated as 67. As in the preceding embodiment, the seat for the disk is surrounded by an annular flange, in this case flange 65, which projects beyond the upper surface of the disk 67. Comparing this with the preceding modification shown in FIG. 4, it will be seen that the constructions are alike in that the flange 50 forms a cavity with the upper surface of the disk 51 in FIG. 4 and in FIG. 6, the flange 65, which surrounds the closure, forms a cavity with the upper surface of the disk 67. This cavity is preferably filled with a cement 68. Preferably the cement is an epoxy resin which, when set, holds the disk 67 in place. The cement used is such as to provide a gas tight joint between the disk and its surrounding flange. This type of cement will not prevent fragmentation of the disks when the gas pressure within the tube 30 causes bursting of the disk. On bursting, the entire opening is cleared of any obstruction to the passage of the button head 55.

Changes in and modifications of the construction described may be made without departing from the spirit of our invention or sacrificing its advantages.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

The combination with an electric fuse having a fuse tube of non-conducting material, an open ended tubular fitting of conducting material mounted on and secured to one end of said fuse tube to form a continuation of the pasage in said fuse tube, of a sleeve detachably secured to the open end of said fitting, said sleeve having an internal flange, a fiat disk of sintered metal particles having the characteristic of disintegrating on failure when subjected to the strain produced by a fluid pressure in excess of a predetermined amount, said disk being seated against said flange, and means forming a gas-tight joint around the edge of said disk capable of holding until failure of said disk under excess pressure.

References Cited by the Examiner UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner. 

